Abstract
Several lines of evidence from post-mortem and neuroimaging studies suggest changes of neuronal plasticity in major depressive disorder. However, direct evidence of impaired neuronal plasticity in depression has not been generated yet. Transcranial direct current stimulation (tDCS) of the motor cortex has been used as experimental paradigm to study non-focal neuronal plasticity and the impact of dopaminergic and serotonergic neurotransmission ( Nitsche and Paulus, 2011 ). Thus, this pilot study investigates whether tDCS-induced non-focal plasticity within the motor cortex is reduced in depression. Non-focal neuronal plasticity was investigated using a combined tDCS-motor evoked potential (MEP) paradigm in 14 patients with a major depressive episode (DSM-IV) compared to 14 healthy subjects matched for age and gender. All patients were free of psychotropic drugs apart from benzodiazepines. Anodal tDCS (2 mA, 20 min) was applied over the left M1 area with the cathode placed over the right supraorbital region. MEP were recorded at baseline and for further 120 min following tDCS. Overall, there was no significant difference in MEP amplitudes between patients and controls. In benzodiazepine-free patients ( N = 8), however, repeated measures ANOVA revealed reduced MEP amplitudes (df = 1, F 23.235, p < 0.001) compared to healthy controls following anodal tDCS. Moreover, a significant correlation was found between benzodiazepine dosage and mean MEP amplitudes ( r = 0.62, p = 0.018). Non-focal motor cortex plasticity by tDCS was reduced in medication-free depressed patients. This finding-if confirmed in a replication trial-would support the notion that neuronal plasticity is impaired in major depressive disorder contributing to the morphological changes revealed by neuroimaging studies.
Published Version
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